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ramifications, that I cannot, in entering upon it, divest myself ofsome feelings of anxiety lest I should fail to do it that justice whichits importance demands. I should not indeed have ventured uponsuch a topic had my previous impressions not been strengthened,and my humble exertions stimulated, by the favourable opinion ofseveral gentlemen on whose more mature judgment I can implicitlyrely; and, even with these advantages, I must, in consideration ofthe difficulties I have had to encounter, and of the short intervalsof leisure which my arduous occupations afford, solicit the indulgenceof my fellow members in behalf of an essay which has grown uponme to an extent which I did not at first anticipate. I have soughteverywhere for documents of a practical nature relating to timberand iron ships—something that I could take as the foundation ofan argument—some historical view of the subject which I couldcarry out and enlarge. Excepting, however, works relating solelyto timber vessels, or some few detached and very imperfect sketchesof iron vessels—and scarcely any, on either subject, of a practicalnature—I could obtain little or no assistance from published docu-ments. I therefore determined to take an independent course, andto trust more to my own observations, and to information derivedfrom those who would kindly assist me in collecting it, than towaste my efforts in a further and, in all probability, a fruitlesssearch. And here permit me to thank several friends, to whom Ihave applied for information, for the uniform readiness with whichthey have replied to all my inquiries, and to state that I shall havemuch pleasure in receiving further additions to the facts I havealready collected, from any one who will favour me by supplyingthem.*

Some explanation may, in the outset, he expected from me, asto the opportunities I have had of forming an opinion on this sub-ject, that those who hear me may he better enabled to judge of thecorrectness of what I shall advance. A few words only are neces-sary on this point. My attention was first directed to the subjectin consequence of my father having, in 1824, caused a small iron

* Since reading this paper to the Polytechnic Society, I have been favoured with severalcommunications, which were, however, too late to be embodied into it under their proper heads.I have therefore inserted some of them as an appendix to the original paper. I beg particularlyto draw attention to the letter of my friend Mr. Fairbairn, as containing the sentiments of a manof great practical and scientific information.